The possibility of using the normal electric power network existing in buildings as a channel for the transmission of electric signals is known. A high-frequency sinusoidal carrier wave which is modulated by the signal to be transmitted is used with systems of the FSK (Frequency Shift Keying) modulation type, i.e. "with frequency shift." This system can be generally identified as the "technique of conveyor waves" or as carrier current transmission.
It is also known for instance in data management of local area networks (LAN), although pertaining particularly to the method of access of the transmission means, to use either techniques of the deterministic type (whereby the access can take place only at predetermined instances), or techniques of the nondeterministic type (based on algorithms which allow the access on a probabilistic basis). To the first category belong methods referred to as "token passing", with register insertion and "time slot" with time intervals. To the second category belong the methods known as "CSMA" (multiple access with carrier detection) and "CSMA/CD" (multiple access with carrier detection/collision detection).
It is also known to use sensors of various types for the detection of one or several presences (intrusions).